Fabrics treated with water repellents tend to lose repellency upon exposure to liquid water, such as rain showers or laundering; and upon exposure to soiling substances, such as oils. Several patents address these problems but without significant success, such as U.S. Pat. No. 4,859,754, 4,716,208, 4,147,851 and 3,997,507. These patents describe copolymers of acrylates or methacrylates having perfluoroalkyl groups, and either amphipathic monomers (U.S. Pat. No. 4,559,754), chlorohydroxypropyl acrylates or methacrylates (U.S. Pat. No. 4,716,202), dialkylamines alkyl acrylates or methacrylates (U.S. Pat. No. 4,147,551) or alkylvinyl ethers (U.S. Pat. No. 3,997,507).
Polymers of acrylic or methacrylic acid esters that have pendant fluoroalkyl side groups are useful as water/oil repellents. The fluoroalkyl groups have the formula --(CH.sub.2).sub.m --(CF.sub.2).sub.n F and typically the polymer will have a distribution of chain lengths wherein n ranges from 4, 6, 8, 10, 12 etc. The component of largest concentration in the polymer is usually predominantly either n=6 or 8 (e.g., typically distributions are by weight, C.sub.4, 4%; C.sub.6 33%; C.sub.8, 30%; C.sub.10, 15%; C.sub.12 8%; etc. or C.sub.6, 2%; C.sub.8, 51%; C.sub.10, 31%; C.sub.12, 11%; etc.). See for example, DuPont Product Literature "Zonyl" Fluorochemical Intermediates.
These polymers can be homopolymers or can be copolymers of the fluoromonomers with other monomers which do not generally detract from the repellent performance, but add other characteristics such as improved film formation or emulsion stability. The distribution of the fluoroalkyl side chain lengths depends on the manufacturing techniques, and the telomers of tetrafluoroethylene used.
The water and oil repellency imparted to substrates coated with these polymers is due to the perfluoroalkyl component, F(CF.sub.2)--.sub.n of the side chain with its terminal CF.sub.3 group. Contact angle measurements carried out by Zisman (Journal of Paint Technology Vol. 44, pp. 42-57 (1972)) indicated these groups have the lowest critical surface tension of wetting known, about 6 dynes/cm., based on perfluorolauric acid monolayer. In addition, A. Owens and R. Wendt have shown (J. App. Poly. Sci. 13 1141 (1969)) that long chain perfluoroalkyl groups have surface energies of 7.8-8 dynes/cm, again a very low surface energy measurement. In the case of fluoroacrylate polymers, the low surface energy of substrates coated with the polymer results from the perfluoroalkyl side chains of the polymers being oriented normal i.e. perpendicular to the surface of the substrate. This maximizes the --CF.sub.3 concentration at the solid/air interface.
However, these polymers tend to lose their effectiveness as repellents over time in contact with water. The loss of repellency can be explained by the molecular rearrangement of these side chains to find a new level of surface energy in a water environment. This alteration of position of the side chains results in a reduction in concentration of the --CF.sub.3 terminal groups at the surface because the --CF.sub.3 groups move away from the most advantageous repellency configuration. Thus, it has long been a defect in existing fluoroalkylacrylate polymers that the oil and water resistance is not as good as it could be because of the mobility of the fluoroalkyl side chains, resulting in the side chains moving or rotating to a less desirable configuration, i.e., to a less chemically uniform configuration on the surface of a substrate. The most desirable configuration is one in which the side chains, as stated above, stick out away from the substrate surface so that the end --CF.sub.3 groups present a chemically uniform barrier to water or oil molecules.